How to set status termination of a process C? - c

Question

My program is a rudimental little shell.
It allow you to run programs in PATH as ls, cd..also with arguments.
To run the program type from terminal "./myshell2" then it starts and you can insert how many commands you want.
It starts a child process, runs execvp,it returns and restarts so you can type a new command.
When typed "Q" or "q" all the entire program should terminates.
The problem is that I don't know how to stop it,the code is below.
My idea is, when typed "Q" or "q", to kill the child process created and send a signal to comunicate its bad termination(of child process).
So the final status(from parent) 'll be not 1 and the function returns.
I commented some parts of the code hoping that it's easier to understand.
It works the problem is that to stop it I need of ctrl C.
I would like to say to child process that he must ends with a non-zero value.
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <string.h>
#include <signal.h>
int main(int argc, char * argv[]) {
while(1)
{
pid_t pid = fork();
if (pid == -1) {
perror("fork error");
exit(EXIT_FAILURE);
}
if (pid == 0) { // child process
printf("type the command to start (and arguments if required) \n"
"Q to quit\n");
char *dest[10]; // allow you to insert
char line[4096];//commands from terminal
if (fgets(line,sizeof(line),stdin)==0) return 1;
int i;
line[strcspn(line, "\n")] = '\0';
char *st = line;
for (i=0; i< 10 && (dest[i]=strsep(&st," "))!=NULL;i++)
continue;//now you typed the command
if ( ( memcmp(dest[0],"Q",1)==0 ) // if Q or q the program
|| (memcmp(dest[0],"q",1)==0) ) //must end
{
printf("got it!\n");
if (kill(getpid(),SIGSEGV)==-1) printf("kill error\n");
//in theory the process should terminates with bad status
// and the value of the variable "status" 'll be not 0
// I think that the problem is in this part of the code
}
if( strcmp(dest[0]," ")!=0 )
{
int res = execvp(dest[0], dest);
}
else
{ int res= execvp(dest[1],dest+1);}
perror("execvp error");
exit(EXIT_FAILURE);
}
int status;
pid_t child = wait(&status);
if (child == -1) {
perror("wait error");
exit(EXIT_FAILURE);
}
if (status==1)
break; //so it can exit from the loop that creates new process
setenv("WAIT","TRUE",0); //dont' worry about
//perror("setenv error\n");
if (memcmp("TRUE",getenv("WAIT"),4) == 0 ) //these 6 lines
printf("WAIT=TRUE\n");
else if(memcmp("FALSE",getenv("WAIT"),4) == 0 )
printf("WAIT=FALSE\n");
printf("end current process (status=%d, child=%d)\n", WEXITSTATUS(status), son);
}
return EXIT_SUCCESS;
}

Answer 1

You're printing out WEXITSTATUS() for all cases, but that isn't right. You need to check if the status returned by wait is an exit status or not using WIFEXITED(). If it's non-zero then the child exited normally. Otherwise, you can use WIFSIGNALED() to see if the child was terminated and you'll get the signal from WTERMSIG()
if(WIFEXITED(status))
{
printf("end current process (status=%d, child=%d)\n", WEXITSTATUS(status), son);
}
else if(WIFSIGNALED(status))
{
printf("end current process (signal=%d, child=%d)\n", WTERMSIG(status), son);
}
You really should have the parent process handle the inputting of the command and leave the child process to run it though.